MM-22051: Remove ToJson methods from network writes (#17999)

We replace the double conversion of
[]byte to string, with a direct write
to http.ResponseWriter.

https://mattermost.atlassian.net/browse/MM-22051

Tried using gofmt -r, but it only accepts Go
expressions. So had to resort to an ugly sed replace

sed -E -i 's/w.Write\(\[\]byte\((.*).ToJson\(\)\)\)/if err := json.NewEncoder\(w\).Encode\(\1\); err != nil { mlog.Warn\("Error while writing response", mlog.Err\(err\)\)}/g' *.go

```release-note
NONE
```

api4/system.go

@@ -260,7 +260,9 @@ func getAudits(c *Context, w http.ResponseWriter, r *http.Request) {
 	auditRec.AddMeta("page", c.Params.Page)
 	auditRec.AddMeta("audits_per_page", c.Params.LogsPerPage)
 
-	w.Write([]byte(audits.ToJson()))
+	if err := json.NewEncoder(w).Encode(audits); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func databaseRecycle(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -397,7 +399,9 @@ func getAnalytics(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Write([]byte(rows.ToJson()))
+	if err := json.NewEncoder(w).Encode(rows); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func getSupportedTimezones(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -539,7 +543,9 @@ func pushNotificationAck(c *Context, w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		w.Write([]byte(msg.ToJson()))
+		if err2 := json.NewEncoder(w).Encode(msg); err2 != nil {
+			mlog.Warn("Error while writing response", mlog.Err(err2))
+		}
 
 		return
 	} else if err != nil {
@@ -600,7 +606,12 @@ func getServerBusyExpires(c *Context, w http.ResponseWriter, r *http.Request) {
 		c.SetPermissionError(model.PermissionManageSystem)
 		return
 	}
-	w.Write([]byte(c.App.Srv().Busy.ToJson()))
+
+	// We call to ToJson because it actually returns a different struct
+	// along with doing some computations.
+	if _, err := w.Write([]byte(c.App.Srv().Busy.ToJson())); err != nil {
+		mlog.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func upgradeToEnterprise(c *Context, w http.ResponseWriter, r *http.Request) {